The invention relates to railroad rail support systems, specifically railroad crossties or ties, and their method of manufacture.
The majority of railroad track today is comprised of wooden crossties, sometimes referred to simply as ties, for alignment and support of iron rails placed thereupon. However, for a variety of reasons, such as the use of lower quality pine rather than oak due to high timber costs, alternatives to wooden crossties have become available to the railroad industry.
These alternative products can be either made of new or recycled materials. Cement, reinforced concrete, metal, recycled wood, plastic, composites of various recycled materials, and other products have been made. A relatively new approach has been to produce a tie from cement having an iron center and encased within recycled rubber and/or recycled plastics.
These alternative products suffer from one or more significant drawbacks. The railroad industry is seeking an economical alternative to wood. Drawbacks encountered with cement and reinforced concrete is that although durable, they weigh substantially more than ties made from wood. Transportation costs are higher and handling is more difficult because of the increased weight. Ties made with a metal core must also be encapsulated with a non-conductive material for safety and operational concerns. Encapsulation is an additional step which increases the cost of the tie.
Another significant drawback to these alternative crossties is the relatively low force required to withdraw a spike driven into the tie. It is highly desirable to have a higher withdrawal force. A higher withdrawal force translates into a more secured spike and reduces or eliminates the need to reset a spike.
Additionally, almost all alternative tie products have increased noise levels as trains pass due to the surface hardness and steel, cement and plastic cross ties also tend to undesirably shift in the gravel bed.
As a consequence, demand from the railroad industry for non-wood ties has been low. It is believed that high demand would exist if a tie could be made for low-cost, have similar performance characteristics, and have a longer life than a wood tie.
In the recycle and rubber tire industries, there has been a concern for many years regarding what to do with discarded tires. A problem facing these industries has been how to recycle discarded rubber products, and especially vehicular tires into useful and economical end products. More information on the various problems relating to the disposal and recycling of discarded tires is provided in the background sections of U.S. Pat. No. 4,726,530 (Miller et. al.) and U.S. Pat. No. 5,094,905 (Murray).
Technology exists for discarded rubber tires to be recycled. Tires are generally comprised of rubber, steel belts and beads, and fiber such as rayon, nylon, and other polyesters. Present technology can shred and granulate tires and have the metal separated magnetically, and the fibers removed by vacuum. The rubber can be shredded or ground into any desired size. This technology is described in the Miller et. al. patent cited earlier. Utilizing separation technology, discarded rubber tires are available as a source for recycled products.
As mentioned earlier, another problem facing the railroad industry is the useful life or longevity of a crosstie before it requires replacement. This concern is even more prevalent today than in the past. Presently in the United States, crossties are mostly made from softwoods such as pine rather than hardwoods such as oak. Softwood crossties do not have the longevity of hardwoods. As an example, softwood crossties are susceptible to accelerated deterioration in high moisture environments. A tie in a swamp area may have an operational life expectancy of only three to four years. It is believed that the railroad industry would be receptive to more durable alternatives to wood where cost savings can be realized.
A method to manufacture railroad crossties from discarded rubber has been developed. The rubber railroad tie can be used as wood tie replacements for new and re-laid tracks. The rubber railroad tie can be made economically and utilize the abundant supply of discarded rubber tires stockpiled at waste disposal sites. A functional new design is disclosed which increases the frictional contact between the crosstie and a gravel bed to prevent undesired crosstie movement.
The rubber railroad crosstie made according to the invention (xe2x80x9cTiexe2x80x9d) is made by a process which heats granulated recycled rubber (sometimes referred to as crumb rubber, rubber dust, or rubber fines), preferably not larger than 30 mesh (590 microns). The heated rubber is preferably milled and then extruded to obtain the desired width and depth and thereafter cut to the desired length.
Recycled crumb rubber (RCR) can be made from discarded tires commonly available at waste disposal facilities. RCR can be made available by type and mesh size.
My invention requires two specific types of RCR. The first type is made from vulcanized rubber. The primary source for vulcanized rubber is from automobile and truck tires. The primary source for the second type is from tires classified as natural rubber or rubber which has been de-vulcanized. Natural rubber tires are mostly off-the-road (OTR) tires, which have less sulfur and zinc content than vulcanized rubber, and have a lower melting point. It is to be understood that there may exist some vulcanized rubber in natural rubber tires. However, the tire industry recognizes this fact and the xe2x80x9cnatural rubber tirexe2x80x9d designation is understood to include some small percentage of vulcanized rubber.
Air pollution is not a concern during the process. The preferred milling and extrusion temperature is between 290-310 degrees F. (143-154 deg C.). At this temperature range, there are no significant amounts of toxic or hazardous gases escaping into the production area or environment. Waste tires and rubber crumbs are not generally classified as hazardous materials; but rather as a waste management disposal problem.
Besides discarded rubber, small additions of polymers may be used in the manufacturing process for strength enhancement. The amount necessary will be dependent upon the actual rubber composition used to form a Tie according to my invention.
It is also possible to produce a rubber railroad crosstie which, in addition to the rubber mentioned above, utilizes the fiber also found in vehicular tires. In other words, a crosstie may be formed using discarded automobile tires provided the steel has been removed.
The Tie can be made by either a compression mold or an extrusion process. The operating pressure for extrusion is dependent upon several factors including the viscosity, screw speed and orifice size. In general, an extrusion process operating between 240-370 degrees F. (116-188 deg C.) should operate in a pressure range of between 250-2,500 psi (1,724-17,240 kPa). Due to the logistical problems associated with a high volume compression mold process, it is more preferable to utilize a continuous extrusion process.
Once formed, the color of the Tie is black. Over time, the surface will oxidize and may turn to an ashen black or gray. Testing has indicated that the Tie is not subject to the level of cracking and product degradation under sunlight as occurs for rubber tires.
My railroad tie is made completely from non-conductive materials. Therefore, no special precautions are necessary as with other ties partially made from metals and which could conduct electricity.
Ties can be manufactured into any length desired and are recyclable.
Creosote, a known carcinogen commonly used in the manufacture of wooden railroad crossties, is not used in the manufacture of the Tie.
The weight of the Tie made according to the invention is, on average, between 13% to 50% less per unit when compared to other railroad tie alternatives to wood. By way of example, for a standard railroad crosstie measuring 8.5 ftxc3x979 inxc3x977 in (259 cmxc3x9723 cmxc3x9718 cm), a crosstie made according to the invention would weigh approximately 278 pounds (126 kg), while one made from concrete would weigh over 500 pounds (227 kg).
A key feature of the Tie is that it can withstand a 120,000 pound (54,480 kg) compression test upon an area equivalent to a standard railroad tie plate of approx 96 square inches (619 sq. cm) Additionally, after the load was removed, no permanent deformation was visible.
The Tie is expected to have a useful life of between 30 to 60 years. The longevity of the Tie will reduce the frequency of crosstie replacement as well as the associated cost for installation.
The Tie can be installed side-by-side a wooden railroad tie. This is in contrast to cement ties and other known alternative crossties where it is recommended that whole-lines be replaced even though only some ties require replacement.
The Tie is designed for attachment in the same way as wood ties. The preferred method is by use of spikes while clips or screws could be used alternatively. The type of attachment would depend on railroad industry preferences for the specific locale in which the track is laid. No new placement or replacement technologies or techniques are required.
Because the Tie is compressed upon formation, further compressive deformation following installation will be minimal. This will permit true alignment during installation. Other crosstie products, including those made from softwoods, have allowances for compression over time to fit the standard rail attachment plates as needed and to grip the gravel under-base or bed.
An optional and unique feature is that the Tie can be made with at least one side having a plurality of indentations or indented surfaces. As used in this specification, xe2x80x9cindented surfacexe2x80x9d and xe2x80x9cindentationxe2x80x9d have the same meaning and are defined here as a non-flat surface. When a plurality of indentations are present on at least one longitudinal side of a crosstie, they collectively are capable of frictionally engaging a bed of gravel better than if the longitudinal side were a flat surface. The indentations must be something more than microscopic deformations which are present on any flat surface; they must be capable of frictional engagement with a gravel bed to prevent the crosstie from slipping or sliding as would be the case if the surface were flat. xe2x80x9cIndentationxe2x80x9d is also defined to include configurations such as ribs, serrations, dimples, and other simple geometric shapes such as diamonds and pyramids which can be indented into the crosstie.
In order to function properly, the indentations must be of sufficient width to permit gravel to enter the concave area. If the indented width were too small, excessive void spaces would form in the concave area and therefore not efficiently frictionally engage the gravel bed.
The decision of whether to incorporate indented surfaces would depend upon the use of the Tie. By way of example, if the Tie were used in high speed rail lines, a gravel bed is not used but rather the crossties are positioned on a hardened surface such as cement. A crosstie having indentations is undesirable in this situation since it would reduce the surface area in contact with the hardened surface thereby reducing frictional engagement.
Where gravel beds are to be used, preferably, one side of the Tie has a plurality of indentations which would face downward when laid. Most preferably, three longitudinal sides of the Tie would utilize indented surfaces. The longitudinal side facing upward when laid need not.
The purpose of having indentations on the Tie is to allow it to better frictionally engage the gravel bed into which it is placed. The depth of each indentation should be limited so as to not affect the structural properties of the Tie; namely, the ability to resist compressive loads.
The indented surfaces will enable the crosstie to resist sliding in the gravel bed as can be the case when aligning crossties having harder and smoother surfaces such as those made from wood, plastic or cement.
The indentations can be formed while the Tie is still hot and receptive to deformation. Alternatively, a Tie which is compression molded can have ribbed sides integrated as part of the mold pattern. Still another way for creating the indentations would be by machining; however this procedure would be expensive in view of the other methods previously discussed.
By way of example, the mechanical properties of a Tie made according to the invention are as follows:
Given that extrusion will yield a crosstie with the above mechanical properties, other applications are possible for this sort of extruded rubber product. By way of example, a crosstie pad, made according to the process described herein, could be positioned between a crosstie and its underbed for train travel noise reduction, and shock absorbency when used in conjunction with either steel, cement or concrete crosstie.